fun mix(s1: String, s2: String) = run {
    val result = hashMapOf<Char, Pair<Int, Char>>() // 字符，多少个字符，谁最多

    fun String.some(i: Char) = asSequence().filterNot { it.isWhitespace() || it.isUpperCase() }.groupBy { it }
            .forEach { (key, v) ->
                v.size.takeIf { it >1 }?.let { size ->
                    result[key] = result[key]?.let {
                        when {
                            it.first < size -> size to i
                            it.first == size -> size to '='
                            else -> it
                        }
                    } ?: size to i
                }
            }
    s1.some('1')
    s2.some('2')

    result.entries.sortedWith(compareByDescending<Map.Entry<Char, Pair<Int, Char>>> { it.value.first }
            .thenBy { it.value.second }.thenBy { it.key })
            .joinToString("/") { "${it.value.second}:${it.key.toString().repeat(it.value.first)}" }
}